Give her an old T-shirt or blanket that has your smell on it and try the old ticking clock trick. Just get an old fashioned wind-up alarm clock (you can get one for less than $10) and set it in the room where she can hear it. Make sure she has a safe chew toy in the crate with her, too. The Orbee-Tuff bone is a good one. Even my huge monsters haven't been able to put a dent in theirs, and they have a wonderful squishy but firm texture that they love and won't hurt puppy gums.
And whatever you do - No Rawhide!
Seven weeks is really at least a week too young to have left her mother, so you're going to have to put some extra time into working with her on things like mouthing and training. She's also going to need extra play time and affection from you since she has left not only her mother, but her littermates early. It's not the end of the world; you just need to be aware and take care of some of the 'puppy learning' her mother would have been teaching her.